Recently, much interest has been directed towards diesel engines due to their inherent fuel efficiency and durability. In order to control diesel emissions to high emissions standards, diesel engine manufacturers and emission-control companies are working on systems and components to achieve stringent emission requirements. One aspect of emission control involves controlling the levels of particulates present in the exhaust stream. For example, diesel particulates are mainly composed of carbon soot. One effective way of removing such carbon soot from diesel exhausts is through use of diesel filters, or combinations of diesel oxidation catalysts (DOCs) and diesel filters. The most widely-used diesel filter is a porous ceramic diesel particulate filter (sometimes referred to as a “wall flow filter”) which filters the diesel exhaust by capturing the soot on or in its ceramic porous walls. The diesel particulate filter is designed to provide soot filtration without significantly hindering the exhaust flow, i.e., without creating significant unwanted back pressure.
Generally, such diesel particulate filters and DOCs include an arrangement of porous ceramic walls forming generally parallel cell channels arranged in a honeycomb configuration. In the case of the filter, at least some of the cell channels are plugged along their length thereby forcing at least a portion of the engine exhaust gas to pass through the filter's porous walls. Such filters may optionally further include a catalyst coating, such as an oxidation or NOx catalyst, on their surface. Various particulate filters are described in U.S. Pat. Nos. 4,329,162; 4,390,355; 4,416,676; 4,509,966; and 4,840,827, for example.
Currently, for various applications, it is desired that such honeycomb filters and DOCs are made to be relatively large; such as 13 inches in diameter, or more. Additionally, to provide low back pressure and to allow the addition of a catalyst coating, it is desirable for the filters to exhibit relatively high total porosity, such as 45% total porosity or more. Generally, to form such high porosities, a large amount of a pore former material must be used. As a result, a significant problem associated with the manufacture of such honeycomb ceramic filters and DOCs due to the large amount of pore former is cracking during drying and/or firing. Thus, it would be considered a significant advancement to obtain a relatively high porosity honeycomb body, especially a large dimension porous ceramic honeycomb body, with a reduced rate of cracking during manufacturing.